Cyril of Jerusalem delivered his Catechetical Lectures on Christian doctrine to his catechumens circa 350 AD. His final five lectures are called Mystagogica (On the Mysteries) and are sometimes reckoned separately. The following quote on the Lord’s Supper is taken from §1, 3, and 6 of the fourth of those final lectures, which is the twenty-second lecture in the entire series. Some of what Cyril says elsewhere in this lecture could easily be understood as sowing the seeds of the modern Roman Catholic doctrine of transubstantiation, and certainly in retrospect it did sow those seeds. However, to the extent that Cyril is cited in support of transubstantiation, he is not being read in context, as the quote below makes clear. He does not assert that the earthly elements have been abolished entirely in the Lord’s Supper, only that they are not “bare.”

Since therefore he has made pronouncement and said with regard to the bread, “This is my body,” who will dare to doubt any longer? And since he has affirmed himself and said, “This is my blood,” who will ever waver, saying it is not his blood? … So then, let us partake with complete assurance that we are partaking of Christ’s body and blood. For in the form of bread, the body is given to you, and in the form of wine, the blood is given to you, in order that, by partaking of Christ’s body and blood, you may be of the same body and blood as he. For in this way we also become Christ-bearers, since his body and blood are distributed throughout our members. … Therefore do not regard the bread and the wine as bare elements, for according to the authoritative pronouncement you are encountering Christ’s body and blood. For even if your senses suggest this to you, it should still be your faith that assures you. Do not judge the matter from what you taste, but from your faith be fully assured without wavering that you have been deemed worthy of being given Christ’s body and blood.